1. Field of the Invention
This invention relates to a control apparatus for a multi-air-conditioner having an external unit and a plurality of internal units, especially to a control apparatus for a multi-air-conditioner which transmits data using a direct current (DC) voltage for a power supply to a transmitting/receiving circuit.
2. Description of the Related Art
Conventionally, a serial transmitting system, in which a plurality of data is transmitted serially in time-series with one signal line, is used for controlling an operation between an external unit and a plurality of internal units of a multi-air-conditioner. An example of a circuit of a related control apparatus for a multi-air-conditioner is shown in FIG. 12. The control apparatus is disclosed in Japanese Unexamined Patent Publication No. SHO 63-306346. In FIG. 12, an external unit 1 is connected to a plurality of internal units 2, 3 and 4, respectively, via commercial power supply lines R, S and a signal line 5. A transmitting/receiving circuit 6 is provided between the commercial power supply line R and the commercial power supply line S in each unit. In the transmitting/receiving circuit 6, a transmitting switch 7 is provided for supplying commercial power (alternating current (AC) power) alternatively according to data transmitted from a controller 9. A signal detector 8 is also provided serially with the transmitting switch 7 in the transmitting/receiving circuit 6 for informing the controller 9 whether the transmitting/receiving circuit 6 is supplied with power or not. Each part of the circuit connecting the transmitting switch 7 and the signal detector 8 in the external unit and the internal units is wired to each other via the signal line 5.
An operation of the circuit of FIG. 12 will be described hereinafter. In the above control apparatus, a photo-coupler is provided with the transmitting switch 7 for supplying the transmitting/receiving circuit 6 with the commercial power alternatively according to data transmitted from the controller 9. The photo-coupler consists of an emitter 71, which emits an optical signal and is driven in a driving circuit 13 connected to an output port PO of the controller 9, and a receiver 72, which receives an optical signal from the emitter 71 and which is capable of supplying or cutting off power supply in both directions.
In the control apparatus, another photo-coupler is provided with the signal detector 8 for supplying or cutting off power to a transistor of a receiving circuit 14 provided in the previous stage of an input port PI of the controller 9. The photo-coupler consists of an emitter 81, which emits an optical signal and is driven by plus/minus AC current passing through the transmitting/receiving circuit 6, and a receiver 82, which receives the optical signal from the emitter 81. The input port PI is set to a high level "H" or a low level "L" according to ON or OFF of the transistor Tr of the receiving circuit 14, which is caused by supplying/cutting off power of the receiver 82.
Data is transmitted to the transmitting switch 7 from the controller 9 synchronously with the commercial power supply. That is, pulsating data is transmitted including a high level "H", which corresponds to a logic level "1" output to the output port PO, and a low level "L", which corresponds to a logic level "0". Transmitting data is synchronized with an integral times of a half-wave of the commercial power supply to output. The data is received at the signal detector 8 by detecting a waveform of plus or minus electric current supplied or cut off to the transmitting/receiving circuit 6 every integral times of the half-wave.
An example of a control apparatus for a separate-air-conditioner including an external unit and an internal unit is shown in FIG. 13. This air-conditioner uses a DC voltage for a power supply to a transmitting/receiving circuit for transmitting data to control an operation between the external unit 1 and the internal unit 2. In FIG. 13, a transmitting/receiving circuit 6 of an external unit 1 is connected to a transmitting/receiving circuit 6 of an internal unit 2 serially via a power supply line S and a signal line 5. AC power "e" is rectified to a DC voltage by a resistance R.sub.1 for dissipating current, a rectifier diode D.sub.1, a Zener diode ZD.sub.1 for restricting voltage and a smoothing capacitor C.sub.1. The rectified DC voltage is about 25 V, so that a semiconductor capable of withstanding a normal voltage can be used in the transmitting/receiving circuit 6. Also in the above rectifying circuit, a leakage distance can be short.
The following elements are connected to the transmitting/receiving circuit 6 of the external unit 1 for protecting the transmitting switch 7 (this transmitting switch 7 is also called "a photo-coupler for external transmission", hereinafter) and signal detector 8 (also called "a photo-coupler for external receipt", hereinafter) against a case of a miswiring: a Diode D.sub.2 capable of cutting off the commercial power; a resistance R.sub.2 for dissipating current; and a diode D.sub.3 capable of cutting off the commercial power for decreasing a voltage of the transmitting switch 7 and the signal detector 8.
To the transmitting/receiving circuit 6 of the internal unit 2, the following elements are connected for protecting the transmitting switch 7 (this is also called "a photo-coupler for internal transmission", hereinafter) and the signal detector 8 (also called "a photo-coupler for internal receipt", hereinafter) against a case of a miswiring: a resistance R.sub.3 ; a diode D.sub.4 capable of cutting off the commercial power; and a Zener diode D.sub.2.
The control apparatus of the device of FIG. 13 differs from the control apparatus of the device of FIG. 12 in having unidirectional photo-couplers in the transmitting switch 7 and the signal detector 8 of the transmitting/receiving circuit 6, respectively.
An operation of the device of FIG. 13 will now be explained.
Transmitting data from the external unit 1 to the internal unit 2 is explained referring to FIG. 14. While the photo-coupler 7 for internal transmission is kept ON, turning the photo-coupler 7 for external transmission ON/OFF causes the photo-coupler 8 for internal receipt to turn ON/OFF to transmit the signal. At this time, the photo-coupler 8 for external receipt is also turned ON/OFF simultaneously.
In FIG. 15, data is transmitted to the external unit 1 from the internal unit 2. While the photo-coupler 7 for external transmission is kept ON, turning the photo-coupler 7 for internal transmission ON/OFF causes the photo-coupler 8 for external receipt to turn ON/OFF for transmitting the signal. At this time, the photo-coupler 8 for internal receipt is also turned ON/OFF simultaneously.
The controller 9 controls transmission of data alternatively in the directions from the internal unit to the external unit or from the external unit to the internal unit.
An operation will now be explained in a case that the commercial power is miswired to the signal line 5 and the power supply line S.
(1) Protection in a case that the signal line 5 of the external unit 1 and the power supply line S are miswired.
(1-1) A period when the signal line 5 is plus and the power supply line S is minus.
In this case, the diodes D.sub.2 and D.sub.3 remain OFF, which causes no influence to the photo-coupler 7 for external transmission and the photo-coupler 8 for external receipt.
(1-2) A period when the signal line 5 is minus and the power supply line S is plus.
In this case, the diode D.sub.3 is turned ON to pass electric current from the diode D.sub.3 to the resistance R.sub.2, however, the diode D.sub.3 is protected by dissipating electric current with the resistance R.sub.2. When the diode D.sub.3 is turned ON, the photo-coupler 7 for external transmission and the photo-coupler 8 for external receipt receive voltage of only V.sub.F from the diode D.sub.3, which hardly influences the photo-coupler 7 for external transmission and the photo-coupler 8 for external receipt.
(2) Protection in a case that the signal line 5 of the internal unit 2 and the power supply line S are miswired.
(2-1) A period when the signal line 5 is plus and the power supply line S is minus.
In this case, the diode D.sub.4 is turned ON to pass electric current to the transmitting/receiving circuit 6. However, the voltage received at the transmitting/receiving circuit 6 is decreased to almost 30 V by the resistance R.sub.3 and the Zener diode ZD.sub.2, thus the photo-coupler 7 for internal transmission and the photo-coupler 8 for internal receipt are protected.
(2-2) A period when the signal line 5 is minus and the power supply line S is plus.
In this case, the diode D.sub.4 is turned OFF to receive all voltages and the Zener diode ZD.sub.2 receives only V.sub.F (almost 1 V). The photo-coupler 7 for internal transmission and the photo-coupler 8 for internal receipt are thus protected.
When a part of the circuit between the signal line 5 and the power supply line R becomes short-circuited, a short-circuit current runs from the transmitting/receiving circuit 6 to the diode D.sub.2, and to the resistance R.sub.2 in the external unit 1. In this case, however, the resistance R.sub.2 dissipates the short-circuit current, and thus the photo-coupler 7 for external transmission, the photo-coupler 8 for external receipt and the diode D.sub.2 are protected.
The control apparatus for the related multi-air-conditioner is configured as described above. In the related art of FIG. 12, the control apparatus includes only one signal line 5 and a pair of commercial power supply lines R and S to transmit and receive data between the external unit 1 and a plurality of the internal units 2-4. However, a transmitting timing of data should be synchronized with the commercial power supply, which causes the transmitting speed of data to be limited to 100 bps (bit per second) at a maximum in a case of commercial power supply 50 Hz, and to 120 bps (bit per second) at a maximum in a case of commercial power supply 60 Hz. In the related art of FIG. 12, commercial power is supplied to each transmitting/receiving circuit 6. The photo-coupler 7 for transmission should have a receiver capable of withstanding a high voltage to supply commercial power bidirectionally or to cut off power. The photo-coupler 8 for receipt should have an emitter capable of being driven bidirectionally. This causes the conventional control apparatus to have a high cost.
When the related art of FIG. 13 is applied to the multi-air-conditioner, a plurality of the circuits of the internal units are connected in parallel. The external unit 1 transmits data to the plurality of internal units 2, and thus the voltage between the signal line 5 and the power supply line S is decreased and enough electric current cannot be supplied to each of the plurality of internal units 2 without an extra circuit.